UARTE STOPRX on exact byte

[parco]

Hi there,

I'm issuing a STOPRX at a specific time but I'm noticing that more bytes are being put into the buffer from after the STOPRX was issued.

Is there a way to stop the UARTE on the exact byte and process, and receive all bytes from that point on to a different buffer?

Please advise.

UPDATE

After triggering a STOPRX, the UARTE will hang around for a few more bytes, placing them in the same buffer and then calling ENDRX. This is problematic since these new bytes are part of a different message.

Here you can see that STOPRX is triggered during some small idle times, yet the ENDRX doesn't happen till much later.

This results in ENDRX being called with 11, 6 and 1 bytes read (when it should be 6, 6 and 6 bytes read)

[RK]

No. The documentation addresses this. if you're using nRF52 (UARTE so I assume so) up to 4 bytes can be received after the STOPRX task. How many actually are depends on what's on the other end transmitting data to you, if it's slow stopping after the RTS signal is deactivated and keeps sending more data, the UARTE is going to receive it. I assume you're using hardware flow control.

Those bytes however go into the RX FIFO so you can update the memory buffer pointer after you get the ENDRX event and then flush to start those bytes off in your new buffer.

[parco]

Thanks @RK. Does any of that change if I'm not using Hardware Flow Control?

Say for instance I had a stream of bytes coming in at 9600 baud, b1 b2 b3 b4 b5 b6 b7 b8 .. bN

If the STOPRX was issued during b5, an ENDRX will fire allowing me to collect b1-b4. Then I can change pointers and issue a FLUSHRX to collect the rest b5-bN?

[RK]

That's covered in the manual as well - they have a note about what happens when you are not using flow control. It's not however clear what happens to a byte in-flight when you stop the UARTE, seems to indicate it stays in the RX FIFO and doesn't get copied via DMA, but it may well depend on how late you stop it.

Not entirely sure what use case this would really matter for however. If you know you want 4 bytes, then set it up to receive 4 bytes and that's what you'll get, and you can update the memory address when you have them and continue. If you don't know until you've read the bytes, set it up to receive more than 4 bytes, stop it, copy anything extra to the start of the buffer, set the pointer up offset by a byte or two if necessary, flush and restart it.

[parco]

I'll give this a shot, thanks!

[parco]

No luck so far, it seems the ENDRX interrupt is being fired about 4 bytes after the stop rx, which doesn't seem to agree with the manual.

The timing is strict with this protocol and I do need to be able to force an ENDRX while still receiving in another buffer. I have a feeling by using STOPRX to do this is causing bytes to be lost.